More on Strings

String Creation and Concatenation

Strings in Python can be created using single quotes (' ') or double quotes (" ").

Example

name = "youtube"
print(name)                 # youtube

Python supports two forms of concatenation:

(1) Implicit Concatenation (Side-by-Side Literals)

Placing two string literals next to each other will concatenate them automatically.

'navin' 'telusko' → 'navintelusko'

Implicit concatenation only works for literals, not variables.

name = 'navin'
name 'telusko'   # ❌ SyntaxError

(2) Using the + Operator

This is the standard and most reliable approach, especially when combining variables with strings.

name = "navin"
print(name + " telusko")    # navin telusko

String Indexing

Strings in Python behave like arrays of characters. Each character occupies a specific position known as an index.

Python supports two indexing systems:

(a) Positive Indexing (Left to Right)

Starts from 0, which represents the first character.

Example:

text = 'telusko'
text[0]   # 't'
text[3]   # 'u'

Requesting an index beyond the string length results in an error:

text[7]   # IndexError

(b) Negative Indexing (Right to Left)

Starts from -1, representing the last character.

Example:

text[-1]   # 'o'
text[-7]   # 't'

Negative indices below the valid range result in an error:

text[-9]  # IndexError

String Slicing

Slicing allows extracting a part of a string using the format:

string[start : end]

• Start index is included
• End index is excluded
• If end is omitted or exceeds length, slicing continues till the end
• If start is omitted, slicing begins at the start

Examples:

text = 'telusko'

text[3:7]   # 'usko'
text[0:3]   # 'tel'
text[2:9]   # 'lusko'   (end exceeds length → safe)
text[2:]    # 'lusko'
text[:4]    # 'telu'

Special Case – Full Slice:

text[:]     # 'telusko'

Slicing makes strings highly flexible and powerful for data extraction.

Strings Are Immutable

In Python, strings cannot be changed after creation.

This means you cannot replace characters using indexing:

text = 'TELusko'
text[0:3] = 'TEL'    # ❌ TypeError

Any transformation like converting to upper or lower case, returns a new string, leaving the original unchanged.

Built-in Functions for String

1. len()

The len() function returns the total number of characters in a string, including spaces and punctuation.

myname = "Navin Reddy"
print(len(myname))  # 11

This is useful for validations, loops, indexing, and data processing.

2. upper()

Converts all characters in the string to uppercase and returns a new string.

text = "Telusko"
new_text = text.upper()

print(text)      # Original → Telusko
print(new_text)  # Uppercase → TELUSKO

3. lower()

Converts all characters in the string to lowercase.

text = "PYTHON Programming"
lower_text = text.lower()

print(text)        # Original → PYTHON Programming
print(lower_text)  # Lowercase → python programming

Multi-line Strings

Python allows multi-line text using triple quotes (""" """ or ''' ''').

Example:

text = """
My name is Navin
Welcome to Telusko
"""
print(text)

Output:

My name is Navin
Welcome to Telusko

Python stores such text with newline characters:

'\nMy name is Navin\nWelcome to Telusko\n'

This is useful for documentation, paragraphs, and formatted text.

Summary

Python provides a rich set of features to work with strings:

• Strings can be created with single or double quotes.
• Concatenation can be done using the + operator or implicit literal joining.
• Indexing allows accessing characters using positive or negative positions.
• Slicing supports extracting meaningful substrings with flexible boundaries.
• Strings are immutable — methods return new values rather than altering originals.
• Multi-line strings allow clean storage of paragraphs and text blocks.
• len() provides an easy way to measure string length.